This invention relates to a thermal clamp for heat forming and/or flattening a titanium sheet and, more particularly, the invention is concerned with providing thermoclamps having parts fabricated of different alloys such that the different coefficients of expansion will operate to apply pressure to the sheet when the clamped fixture is heated.
Heretofore, it has been common practice to heat flatten or form titanium sheets by heating in an oven. There are three variable elements that affect the procedure. These elements are heat, time and pressure. In the production of flattened and formed titanium the heat is limited to the 1200.degree. F. to 1250.degree. F. range so that the recrystallization annealed properties will not be disturbed. The time is limited to about one hour at temperature in the interest of keeping the cost reasonable. Thus, in effect, the only element which is variable is the pressure.
Normally, components of a heat treat fixture are fabricated of the same alloy and the necessary clamping action is accomplished by wedges which are driven into slots to apply pressure. These wedges loosen up during the heating cycle requiring the fixture to be removed from the oven at peak temperature. The wedges must then be redriven and the heat treat fixture reinserted into the oven for the balance of the cycle. Thus, it can be seen that, presently, the production of flat recrystallization annealed titanium is dependent upon wedge activated clamps which loosen up during the hot sizing and forming operation in the fixture run in the oven. Also, the inability of titanium producers to supply flat recrystallization annealed conditioned 5A1-4V titanium forces airframe builders to purchase excess on each side of a plate and machine it flat. In certain cases such as, for example the B1 bomber, this excess can amount to 6200 pounds per aircraft.